1. Field of the Invention
The invention concerns a modular placement device of a feed station. Such a feed station is an apparatus within a mail processing system that is equipped to feed mail pieces or flat goods to a printing apparatus. The invention is designed to simplify the feed station that is arranged upstream (in terms of the mail flow) of a peripheral apparatus (enveloping station, moistening/closing station, dynamic scale) or a printing apparatus. The modular placement device is required upstream (in terms of the mail flow) of a feed station without a placement region, and is suitable for use in a mail franking station in connection with a franking machine arranged downstream (in terms of the mail flow) of the feed station.
2. Description of the Prior Art
A system to frank mail shipments is known from DE 27 17 721. A stack of mail pieces that are stacked atop one another in an arbitrary order is placed in a magazine in the placement region. The stack is placed to the rear of a guide wall of the feed station, such that the edges of the mail pieces lie flush with the front side and rear side of the stack. The stack is situated at the start of a transport path and presses the lowermost mail piece against a feed deck. The lowermost mail piece forms the start of the stack and should first be isolated in the transport direction. To assist with the isolation, a wedge is applied to the stack from the left (upstream side). The surface of the wedge forms a sloped plane with an angle of inclination relative to the horizontal plane of the feed deck. A downhill slope force (grade) that is dependent on the cosine of the angle of inclination and the weight of the stack acts in the transport direction along the sloped plane. It is disadvantageous that the angle of inclination must be large enough and the letter length must be adjusted accordingly, or that the downhill slope force must be set dependent on the length of the mail piece. This hinders the feed for what is known as mixed mail, i.e. a mail stack with mail pieces of respectively different formats and thicknesses. An interference-free effect of the wedge also requires a defined minimum weight of the stack or of the mail pieces as well as a certain rigidity of the mail pieces so that their curvature is slight. Given an interference-free effect of the wedge at the right side of the stack, the edge of the lowermost mail piece projects the farthest, is thus engaged first and is pulled from the stack.
A device to isolate flat articles of different thickness and size from a stack is known from the German Utility Model DE 29823055 U1. The device is essentially subdivided into a placement region and into an ejection region, which follows the placement region to the right in the transport direction. Adjoining the placement region to the left is a wedge-shaped stack receptacle, and to the right a stack stop. A removal device in the ejection region has a height-adjustable retaining means and ejection rollers. A stack of flat goods (mail pieces) to be printed presses the lowermost mail piece in the placement region at the start of the transport path against the feed deck. If the stack is inclined and high enough, the contact pressure force exerted by the weight of the upper mail pieces on the lowermost mail piece contributes to an isolation (separation) of the lowermost mail piece. Interruptions in the isolation can occur, however, if the contact pressure is too high or if, in spite of a suitable stack height, the mail piece is only insufficiently pressed against the feed deck. Such disruption of the passage of the flat goods should be avoided or be simple to remedy.
In the German Patent DE 196 05 017 C2, an arrangement to pre-isolate print media is disclosed that breaks up the stack by means of projections at a drive roller its rotation. Since the arrangement also has a spring-biased pressure hoop that presses the stack of mail pieces against a guide plate, due to the spring pressure between the mail pieces a stiction (static friction) occurs that counteracts relative motion between the mail pieces. Upon reaching the maximum retention force, the relative motion is prevented. This retention forces:FRmax=μH·F  (1)with an elastic force F and with a coefficient of friction μH that depends on the material properties or the surface condition of the mail pieces. The elastic force of a spring is proportional to its deflection. The stiction therefore increases with the height of the stack, i.e. the more that the pressure clip is deflected, thus is spaced from the guide plate. The maximum retention force is achieved even before the pressure clip is maximally deflected. By loosening the stack, the stiction is temporarily overcome so that the individual mail pieces can easily be drawn from the stack. Loosening of the stack is superfluous given a low stack height of mail pieces of the same format. The cost for an actively operating device, which requires an actuator for a pre-isolation via drive rollers, is disadvantageous. However, a pressing on the stack is required if mixed mail, or even bulky or twisted mail pieces are included in the stack. The non-uniform pressure force is disadvantageous during the processing of the stack by the isolation of the mail pieces, in which case the pressure force increases with the stack height.
In a franking system with the Ultimail franking machine that is commercially available from Francotyp-Postalia, an automatic feed station is used for stacks of mail pieces lying on their back sides. The recommended maximum stack height is 50 mm. Given a higher stack level, a stiction can occur between the mail pieces, which in individual cases prevents an isolation. 30 to 40 mail pieces per stack can be anticipated. For example, the mail pieces are enveloped letters with the C6 envelope format in terms of length and with an average weight of 20 g per piece. A total weight of 600 g to 800 g therefore results for a stack with maximum stack height.